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Suicide inactivation of the E. coli O6‐methylguanine‐DNA methyltransferase.
Author(s) -
Lindahl T.,
Demple B.,
Robins P.
Publication year - 1982
Publication title -
the embo journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.484
H-Index - 392
eISSN - 1460-2075
pISSN - 0261-4189
DOI - 10.1002/j.1460-2075.1982.tb01323.x
Subject(s) - biology , methyltransferase , o 6 methylguanine dna methyltransferase , dna , microbiology and biotechnology , escherichia coli , genetics , methylation , gene
The O6‐methylguanine‐DNA methyltransferase of Escherichia coli acts rapidly and stoichiometrically to convert a mutagenic O6‐methylguanine residue in DNA to unsubstituted guanine. Even at low protein concentrations and in the absence of any cofactors, the transfer of a methyl group to one of the protein's own cysteine residues occurs in less than 2 s at 37 degrees C. The entire kinetic process can be followed experimentally at 5 degrees C. Formation of S‐methylcysteine in the protein is accompanied by loss of activity and accounts for the exceptional suicide kinetics of this enzyme as well as for the sharp saturation of O6‐methylguanine repair observed in vivo. The enzyme can remove greater than 98% of the methyl groups from O6‐methylguanine present in alkylated DNA, but leaves N‐alkylated purines untouched. Single‐stranded DNA containing O6‐methylguanine is a poor substrate, with the methyl transfer occurring at approximately 0.1% of the rate for duplex DNA. This latter observation may explain the high frequency of mutations induced by alkylating agents at DNA replication forks.